The present invention relates to a connection adapter between a rigid transcutaneous implant, which can be anchored intracorporeally in a femoral stump, and a part of an extracorporeal orthopedic knee joint.
A transcutaneous implant of this type is known from DE 198 26 638 C2. The adapter disclosed therein for an exoprosthetic standard part can be seated with a proximal stem part in a tubular bone stump, the stem part being covered at least partly by an open-meshed, three-dimensional spatial network structure and being provided at its distal end with a coupling device for the exoprosthetic standard part. The open-meshed, three-dimensional spatial network structure, which is also referred to as interconnecting, makes it possible for natural bone material to grow in, through, behind and around it during the healing phase in such a way that the stem part is integrated into the tubular bone, in any case with respect to the substrate flow, within a relatively short period of time, and an extremely stable secondary fixation is ensured. The distal end of the implant exits from the stump of the limb and provides a coupling option for an exoprosthetic standard part, for example an extracorporeal orthopedic joint.
The immediate perception thus obtained of external skeletal loading of the patient is referred to as osseoperception. This affords the patient, for example a thigh amputee, a completely different type of perception.
The connection between the adapter and the natural bone can, however, turn out to be so strong that even this desired strength can lead to problems, namely if there is extreme exposure to forces. From the outset it cannot therefore be ruled out that an extreme, for example shear, loading of the artificial knee joint or a loading of the lower-limb prosthesis will be transferred into the intramedullary anchored adapter in the femoral stump where it may lead to fracturing. For this purpose it was proposed in EP 1 309 297 B1 to form a leg prosthesis of this type in such a way that it comprises a predetermined breaking point arranged extracorporeally that permits the prosthesis part to break off upon application of a force of predetermined magnitude. This type of described predetermined breaking point is intended to break in the event of a torsional or tilting moment.
However, any torsional moments applied about the femur-tibia axis are even more critical. If excessive torsional moments are applied, this may lead to a spiral fracture above the implant anchored in the femoral stump. Torsional moments of this type may ultimately lead to fractures of the femoral neck.
This should naturally be avoided. A connection adapter of the above-mentioned type is developed in such a way that, where possible, torsional moments applied about the femur-tibia axis no longer lead to spiral fractures in the femoral stump.